Directional gecko-adhesive gripper systems conventionally use either tendons or foam to load the adhesives. String tendons are routed and glued to three-dimensional, pre-drilled holes on the corner of fiberglass backings, which are difficult to manufacture and scale up. These tendons are only attached to the adhesive tiles along the preferred shear direction (X axis), which optimizes the load in the X-Z (preferred-shear-normal) plane, but limits the loading capability in the Y (lateral shear) direction. For example, the resulting X (preferred shear) capability of such systems is usually 2-3 times larger than the shear capability in the Y (lateral shear) direction. Also, fiberglass backings are difficult to make and cut, especially with adhesives attached. Further, foam can lead to non-uniform loading on the adhesive patches, which can reduce the overall adhesive capability and can cause creeping problems. For example, when a gripper is held under a moderate load for a long time, failure may gradually propagate throughout the adhesive patches, making the adhesive capability time dependent. Foam, which is usually placed on top of the adhesives, also contributes to an extra moment load that tends to peel the adhesives off from the surface. No previous directional and controllable gecko-adhesive grippers can be scaled up for mass production due to sophisticated design and large amounts of labor required.
There exists a need for a directional and controllable gecko-adhesive gripper that can handle equal amount of load in all shear directions and can be scaled up for mass production. The present gripper system with rigid backing and three non-stretchable flexible film pieces as actuation element can be easily scaled up for mass production with much lower cost and much larger loading capability than previous controllable gecko gripper systems.